The coronary arteries of the cat will be perfused while nervous activity in afferent and efferent cardiac sympathetic and vagal nerve fibers is monitored. Discharge patterns during changes of coronary arterial and venous pressure, and during myocardial ischemia will be studied. The inter-relationship between medullary inhibitory and spinal excitatory reflex initiated by coronary receptors will be determined. The precise mechanisms whereby ischemia receptors and mechanoreceptors are excited will also be investigated. A simpler model for the study of neurocirculatory control will be sought using the marine mollusc Aplysia Californica.